The present invention relates to the domain of spinal osteosynthesis intended for surgery of the vertebral column, to correct malformations of the degenerative or idiopathic, neuromuscular or tumoral, or of the traumatological type.
In prior art, it is known how to use an instrumentation comprising implants to be fixed on the bone, by screwing or by hooks and linkage elements enabling the surgeon to apply constraints for straightening or stabilising the vertebral column.
As an example, the European patent EP626828 describes such a system enabling osteosynthesis on the vertebral column, together with a linkage element between this system and the tools used for assembly and/or disassembly. This prior art document describes a device for osteosynthesis on the vertebral column, in particular for stabilising the vertebrae, comprising:                at least one linkage element in the shape of a rod.        at least two fixation elements each able to be anchored in a vertebra, these means having a head of the forked shape type whose two branches define a reception space closely U-shaped for the linkage element,        a tightening screw able to be screwed in the reception space to fix the linkage element between the two branches of the fork-shaped screw head,        the head whose bottom of the reception space is shaped in the form of a concave cup corresponding with a tilting bushing element fitted between the bottom of the reception space and the linkage element, the bushing element whose bearing surface opposite the reception space bottom is of a complementary convex shape, characterised in that the tilting bushing element is provided with a hemispherical bearing surface corresponding with the bottom of the reception space. This element is provided with a cut-out open from the tightening screw side in order to receive the linkage element in the form of a rod. The tilting bushing is maintained against the bottom of the reception space in such a way that it can tilt just as well in a plane parallel to the median plane of the reception space as in a perpendicular plane.        
Patent PCT WO9101691 is also known, describing a device for straightening and propping up a vertebral column, constituted of screwed implants or hooks linked by at least two rods integrated together through the intermediary of connection and linkage elements. These rods are introduced longitudinally in grooves perpendicular to the screw, provided for this purpose in the body of the implants or hooks, then blocked in the bottom of the grooves. Integralisation of the rods is obtained with a threaded cross tie. A deformation by approaching the sides of the groove, set in the body of the implants or hooks, in order to obtain blocking of the rod in the bottom of the groove, is obtained through a system of cylindrical screw and conical threaded nut.
Patent WO9514437 is also known, revealing an implant comprising a part destined for anchoring the bone and a body for fixation on a rod, comprising two lateral branches defining a channel, this implant also comprising a threaded plug adapted in order to be screwed on the internal walls of the two branches. Another patent PCT WO9410944 describes a device comprising a connection element set between a rod or other longitudinal implant, and a bone fixation screw placed in the degenerative vertebra. This connection element comprises a ring with dimensions such that the rod can pass through. The ring is provided with screws for fixing the rod and extends radially thanks to a cylindrical arm designed to be fixed to the fixation screw of the bone and tightened on the screw. The arm and the ring constitute a single part. This device allows the surgeon to avoid deforming the rod further when the latter is in the presence of non-aligned vertebral pedicles, leaving the surgeon total freedom to choose the placing of the two axes of the fixation screw of the bone and the rod.
The problem of devices of prior art is that of maintenance of the orientation decided by the surgeon at the time of the definitive fixation and of the dissociation between the positioning of the linkage element and the insertion of the bone implant. In the devices comprising a tightening screw, the tightening of this screw has a tendency to modify the relative orientation of the linkage rods and the fixation element.
Another problem is that of adjusting the setting of the screws during the realignment stage of the vertebral column by rotation of the correction rod. This correction rod crosses through numerous vertebral implants, for example 10 to 15 implants and/or vertebral screws. Generally, each of these implants comprises a blocking screw. This blocking screw must be sufficiently tightened to avoid slipping from the vertebral implant, but not too tight in order to allow rotation of the rod without excessive friction. The adjustment of the degree of screwing of each of these blocking screws is a fastidious and delicate operation.